Optical Networks

So what is this thing called an optical network? Well in its most basic sense it is just some flashing light traveling down a glass rod. The purpose of this flashing light is to transmit information, in much the same way that an old man flashing himself in a dark alley is conveying information to you. But an optical network can give much more useful information than "Hey, look at me, fancy a piece of this?" In fact, an optical network can transmit any information you can imagine — phone calls, videos, music, live TV transmissions, and even this very Web page.

All of these sources of information can be transmitted over long distances by regular electrical signals traveling over copper cables. The key to an optical network compared with an electrical network is that the amount of information that can be transferred is vastly increased. Back in the days when our only needs were the occasional phone call, electrical networks could more than handle the demand. But today, with the great amount of information that needs to be transmitted across and between countries, optical networks are by far the most cost-effective solution.

So an optical network just consists of large glass rods connecting different locations with monkeys at either end switching flashlights on and off? Hmmm... not quite, but the principle is similar. Instead of glass rods we have optical fibers. These are incredibly thin strands of glass (similar in diameter to one of your hairs) that can be many hundreds or even thousands of miles long. They connect different locations that are part of the “optical network.” The optical fiber is packaged up and protected in a surrounding cable, and then usually laid underground or even underwater.

If you tried shining a flashlight down a short glass rod, very little light would actually make it to the other end. And so to make an optical network that can carry information over such huge distances there are two things to be improved. Firstly, the glass that forms an optical fiber is specially designed to be able to transmit light for very long distances (it has “low loss” or “low attenuation”). Secondly, the light sent through the fiber is very high intensity laser light, capable of traveling much farther than regular light.

The laser light flashes on and off in a pattern that represents the information being sent. You can think of this as being similar to Morse code, where certain series of dots and dashes form information. The quicker the lasers can flash on and off, then the quicker the information can be transferred. The speed of transfer is known as “bit-rate” and is usually talked about in terms of bits per second — bps or bit/s (effectively the number of flashes possible per second). Modern networks can transmit 10 Gbit/s from one single laser — 10 Gigabits per second, which is 10 billion flashes per second. To put this into context, you could send the text of more than 1000 books in just one second.

At the other end of the optical fiber is a light detector that senses the on-off flashes of light and converts them back into regular information — whether that’s, say, a sultry voice in a premium phone call or an image on a Web page.

The way that an optical network is generally used is that there will be optical fiber links between most large countries, between most large cities in a country, and then out from each of those cities to the smaller towns. However, electrical signals traveling down copper cables are usually still used for the relatively small amount of information that needs to be transmitted from our individual homes, although a larger business may have its own optical fiber link into the country's optical network.

Key Points

Further Reading

Optical Fiber, Laser Basics, Wavelength Division Multiplexing (WDM), Submarine Systems